Denitrification process and denitrification system for rare earth tail water

Abstract

The present application provides a kind of denitrification process and denitrification system of rare earth tail water.The denitrification process includes: step S1, the pretreatment of rare earth tail water is carried out, and pretreated tail water is obtained;Step S2, pretreated tail water is subjected to multiple partial nitrification-anammox denitrification treatment, and primary denitrification wastewater is obtained;And step S3, primary denitrification wastewater is subjected to CANON process denitrification, and denitrification water and sludge are obtained.The above method is subjected to multiple partial nitrification-anammox denitrification treatment and CANON process, so that the nitrogen in rare earth tail water is converted into N2 and removed, achieving the purpose of wastewater denitrification.And the advantages of partial nitrification-anammox are fully retained in the above process, and effective denitrification can be achieved without adding organic carbon source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth tail water treatment, in particular to a denitrification process and system for rare earth tail water. BACKGROUND

[0002] Rare earth tail water has the characteristics of high ammonia nitrogen, low COD and high salinity. In China, the traditional A / O process is mainly used for biological denitrification of rare earth tail water. The A / O process belongs to the full nitrification and denitrification biological denitrification technology. Due to the limitation of the internal circulation rate of the A / O process, the denitrification efficiency is limited. At the same time, a large amount of organic carbon source needs to be added as an electron donor to convert nitrate (NO3 - ) into nitrogen (N2) in the denitrification stage, which has the disadvantages of high energy consumption, high operation cost, high sludge production rate and the like.

[0003] In recent years, with the progress of technology and in-depth research, new biological denitrification technologies such as short-cut nitrification and denitrification, simultaneous nitrification and denitrification, and anaerobic ammonia oxidation technology have made breakthrough progress and have entered the stage of industrial application. Partial nitritation-anaerobic ammonia oxidation denitrification process is a new type of high-efficiency biological denitrification technology. Compared with the traditional nitrification and denitrification, partial nitritation-anaerobic ammonia oxidation has the characteristics of low energy consumption, low cost, low pollution and high efficiency. SUMMARY

[0004] The main purpose of the present application is to provide a denitrification process and system for rare earth tail water to solve the problems of high energy consumption and high cost in the prior art. In order to achieve the above purpose, according to one aspect of the present application, a denitrification process for rare earth tail water is provided, which comprises: step S1, pretreating the rare earth tail water to obtain pretreated tail water; step S2, performing partial nitrification-anaerobic ammonia oxidation denitrification treatment on the pretreated tail water to obtain primary denitrification wastewater; and step S3, performing CANON process denitrification on the primary denitrification wastewater to obtain denitrified water and sludge, and step S2 comprises: step S21, performing partial nitrification reaction on the pretreated tail water to convert part of the ammonia nitrogen in the pretreated tail water into nitrite nitrogen to obtain a first mixed liquor, wherein the dissolved oxygen is controlled to be between 0.5-2.0 mg / L; step S22, performing sludge-water separation A on the first mixed liquor to obtain concentrated sludge and supernatant; step S23, performing anaerobic ammonia oxidation denitrification reaction on the supernatant to obtain a second mixed liquor; and step S24, returning at least part of the second mixed liquor to step S21 for continuous partial nitrification reaction, and the ammonia nitrogen concentration of the primary denitrification wastewater obtained in step S23 is below 30 mg / L.

[0005] Further, the concentrated sludge is returned to step S21.

[0006] Further, in the step S21, the pH is controlled between 8.0 and 8.5, the mixed liquor suspended solids concentration is controlled between 2000 and 4000 mg / L, and the hydraulic retention time is controlled between 3 and 6 h.

[0007] Further, in the step S23, the dissolved oxygen is controlled to be ≤0.5 mg / L, the mixed liquor suspended solids concentration is controlled between 2000 and 4000 mg / L, the hydraulic retention time is controlled between 2 and 4 h, and the temperature is controlled between 25 and 40℃.

[0008] Further, in the step S24, the recycle ratio of the second mixed liquor is controlled to be 50-300%.

[0009] Further, the step S3 comprises: a step S31, subjecting the primary denitrified wastewater to CANON denitrification treatment to obtain a third mixed liquor; and a step S32, subjecting the third mixed liquor to sludge-water separation B to obtain sludge and denitrified water, and preferably, the sludge is backflowed to the step S31.

[0010] Further, the step S31 is performed in a CANON biofilm reactor, preferably, the CANON biofilm reactor is filled with suspended fillers and activated sludge containing ammonia-oxidizing bacteria, and the suspended fillers embed anaerobic ammonia-oxidizing bacteria.

[0011] Further, in the step S31, the dissolved oxygen is controlled to be between 0.2 and 0.8 mg / L, the pH is controlled to be between 7.8 and 8.5, the mixed liquor suspended solids concentration is controlled to be between 2000 and 4000 mg / L, and the hydraulic retention time is controlled to be between 4 and 6 h.

[0012] Further, the step S1 comprises: a step S11, reducing the turbidity of the tail water by coagulation sedimentation; and a step S12, adjusting the pH of the rare earth tail water to 8.0-10 to obtain pretreated tail water, and preferably, the turbidity of the effluent of the step S1 is controlled to be ≤5 NTU.

[0013] According to another aspect of the present application, there is provided a denitrification system for rare earth tail water, comprising: a pretreatment unit for pretreating the rare earth tail water to obtain pretreated tail water; a partial nitrification-anammox denitrification unit connected to the pretreatment unit, for performing partial nitrification-anammox denitrification treatment on the pretreated tail water to obtain primary denitrification wastewater; a CANON denitrification unit connected to the partial nitrification-anammox denitrification unit, for performing CANON process denitrification on the primary denitrification wastewater to obtain denitrified water and sludge, the partial nitrification-anammox denitrification unit comprising: a partial nitrification treatment device connected to the pretreatment unit, the partial nitrification treatment device having a first mixed liquor outlet and a second mixed liquor reflux inlet, and preferably the partial nitrification treatment device further has a concentrated sludge reflux inlet; a first sedimentation tank having a first mixed liquor inlet, a concentrated sludge outlet and a supernatant outlet, the first mixed liquor inlet being connected to the first mixed liquor outlet, and the concentrated sludge outlet being connected to the concentrated sludge reflux inlet; an anammox denitrification treatment device having a supernatant inlet, a second mixed liquor outlet and a primary denitrification wastewater outlet, the supernatant inlet being connected to the supernatant outlet, the second mixed liquor outlet being connected to the second mixed liquor reflux inlet, and the primary denitrification wastewater outlet being connected to the CANON denitrification unit.

[0014] Further, the CANON denitrification unit comprises: a CANON biofilm reactor having a primary denitrification wastewater inlet, a third mixed liquor outlet and a sludge reflux inlet, the first denitrification wastewater being connected to the partial nitrification-anammox denitrification unit, and preferably the CANON biofilm reactor is filled with suspended fillers and activated sludge containing anammox bacteria, the suspended fillers embedding the anammox bacteria; a second sludge sedimentation tank having a third mixed liquor inlet, a sludge outlet and a denitrified water outlet, the third mixed liquor inlet being connected to the third mixed liquor outlet, and the sludge outlet being connected to the sludge reflux inlet.

[0015] Further, the pretreatment unit comprises: a conditioning tank provided with a pH value adjusting dosing device and having a conditioning water outlet; a coagulation tank provided with a coagulant dosing device and a flocculant dosing device and having a conditioning water inlet and a pretreated water outlet, the conditioning water inlet being connected to the conditioning outlet, and the pretreated water outlet being connected to the partial nitrification-anammox denitrification unit.

[0016] By using the technical solution of the present application, the nitrogen in the rare earth tail water is converted into N2 and removed through multiple partial nitrification-anammox denitrification treatment and CANON process, so as to achieve the purpose of wastewater denitrification. Moreover, the advantages of partial nitrification-anammox are fully retained in the above process, and effective denitrification can be achieved without adding organic carbon source. BRIEF DESCRIPTION OF DRAWINGS

[0017] The drawings constituting a part of the specification illustrate the present application, the exemplary embodiments of the present application and its description serve to explain the present application, and do not constitute an undue limitation on the present application. In the drawings:

[0018] Figure 1 A flowchart of a rare earth tail water denitrification process is shown according to an embodiment of the present application; and

[0019] Figure 2 A structural diagram of a rare earth tail water denitrification system is shown according to an embodiment of the present application.

[0020] Among the above drawings, the following reference signs are included:

[0021] 10: pretreatment unit; 20: partial nitrification-anaerobic ammonia oxidation denitrification unit; 30: CANON denitrification unit; 11: conditioning tank; 12: coagulation tank; 21: partial nitrification treatment device; 22: first sedimentation tank; 23: anaerobic ammonia oxidation denitrification treatment device; 31: CANON biofilm reactor; 32: second sludge sedimentation tank. DETAILED DESCRIPTION

[0022] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] As analyzed in the background, the existing processing technology of rare earth tail water has the disadvantages of high energy consumption, high operation cost, high sludge yield, etc. The partial nitritation-anaerobic ammonia oxidation denitrification process is a new type of high-efficiency biological denitrification technology, which has the characteristics of low energy consumption, low cost, low pollution and high efficiency, but because the nitration reaction process is difficult to control, the accumulation rate of nitrite is unstable, and it cannot meet the specific ammonia nitrogen and nitrite ratio (NH3-N / NO2 - -N) requirement of the anaerobic ammonia oxidation unit influent. In order to solve this problem, the present application provides a denitrification process and system for rare earth tail water.

[0024] In a typical embodiment of the present application, a denitrification process for rare earth tail water is provided, as shown in Figure 1As shown, the denitrification process includes: step S1, pretreating the rare earth tail water to obtain pretreated tail water; step S2, performing partial nitrification-anaerobic ammonia oxidation denitrification treatment on the pretreated tail water to obtain primary denitrification wastewater; and step S3, performing CANON process denitrification on the primary denitrification wastewater to obtain denitrified water and sludge, and the step S2 includes: step S21, performing partial nitrification reaction on the pretreated tail water to convert part of the ammonia nitrogen in the pretreated tail water into nitrite nitrogen to obtain a first mixed liquor, wherein the dissolved oxygen is controlled to be between 0.5-2.0 mg / L; step S22, performing sludge-water separation A on the first mixed liquor to obtain concentrated sludge and supernatant, and the concentrated sludge is preferably returned to step S21; step S23, performing anaerobic ammonia oxidation denitrification reaction on the supernatant to obtain a second mixed liquor; and step S24, refluxing at least part of the second mixed liquor to step S21 to continue the partial nitrification reaction, and obtaining the primary denitrification wastewater from step S23, and the ammonia nitrogen concentration of the primary denitrification wastewater is below 30 mg / L.

[0025] The present application adopts a multi-step method to denitrify the rare earth tail water. First, the rare earth tail water is pretreated to provide suitable water quality conditions for subsequent processing steps. Second, the pretreated tail water is subjected to partial nitrification-anaerobic ammonia oxidation denitrification treatment, which is divided into three steps: (1) the rare earth tail water is subjected to partial nitrification treatment to obtain a first mixed liquor containing ammonia nitrogen and nitrite nitrogen, and this step does not require strict control of the ratio of ammonia nitrogen and nitrite nitrogen in the first mixed liquor. (2) Subsequently, anaerobic ammonia oxidation denitrification treatment is performed, most of the nitrite nitrogen and part of the ammonia nitrogen are removed, and a second mixed liquor containing ammonia nitrogen is obtained. (3) The second mixed liquor is refluxed to the front-end partial nitrification reaction unit to continue the nitrification reaction, and thus the cycle treatment mixed liquor is obtained through multiple cycles. Finally, the cycle treatment mixed liquor is subjected to further denitrification treatment in the CANON process to obtain wastewater meeting the ammonia nitrogen and total nitrogen standards. Most of the unreacted ammonia nitrogen in the anaerobic ammonia oxidation denitrification treatment is converted to N2 and removed in the subsequent CANON process, achieving the purpose of wastewater denitrification. Moreover, the above process fully retains the advantages of partial nitrification-anaerobic ammonia oxidation, and can effectively denitrify without adding organic carbon source.

[0026] During partial nitrification, dissolved oxygen is controlled between 0.5 and 2.0 mg / L, allowing ammonia oxidation to be controlled at the nitrite stage without strictly controlling the ammonia nitrogen to nitrite ratio. After partial nitrification, the resulting first mixture undergoes sludge-water separation A to obtain concentrated sludge and supernatant. Step S24, after repeatedly refluxing the second mixture for partial nitrification, further reduces the ammonia nitrogen concentration in the wastewater to below 30 mg / L, forming primary denitrification wastewater for the next treatment step. This embodiment reduces the difficulty of controlling the partial nitrite reaction process and offers advantages such as high efficiency, energy saving, and flexible control.

[0027] In one embodiment, the sludge is preferably returned to the partial nitrification step to maintain the concentration of suspended solids in the mixed liquor in the partial nitrification unit.

[0028] In the partial nitrification process, the oxidation of ammonia nitrogen uses O2 as an electron acceptor. Therefore, the oxygen concentration affects the treatment effect of partial nitrification. At the same time, other physicochemical parameters and process parameters also affect the treatment effect. In order to improve the treatment effect of step S21, it is preferred that the pH in step S21 be between 8.0 and 8.5, the concentration of suspended solids in the mixed liquor be between 2000 and 4000 mg / L, and the hydraulic retention time be between 3 and 6 h.

[0029] In the anaerobic ammonia oxidation denitrification reaction, nitrite nitrogen acts as an electron acceptor, oxidizing ammonia nitrogen to N2. Therefore, in step S23, the dissolved oxygen is preferably controlled at ≤0.25 mg / L. Simultaneously, the mixed liquor suspended solids concentration is preferably between 2000 and 4000 mg / L, the hydraulic retention time between 2 and 4 hours, and the temperature between 25 and 40°C to ensure the efficient conduct of the anaerobic ammonia oxidation denitrification reaction.

[0030] To ensure the removal efficiency of the denitrification process, it is preferable that the circulation ratio of the second mixture in step S24 above is 50-300%.

[0031] In one embodiment, step S3 preferably includes: step S31, performing CANON denitrification treatment on the primary denitrification wastewater (i.e., corresponding to...). Figure 1 In step S31, the third mixed liquor is obtained through CANON biofilm treatment. In step S32, the third mixed liquor is subjected to sludge-water separation B to obtain sludge and denitrified water. Preferably, the sludge is returned to step S31. By performing sludge-water separation B and returning the sludge to the CANON denitrification process, a suitable suspended solids concentration in the mixed liquor in the reactor can be maintained, ensuring the denitrification efficiency of the reactor.

[0032] Preferably, the step S31 is performed in the CANON biofilm reactor 31, preferably the CANON biofilm reactor 31 is filled with the suspended packing (such as fixed or suspended biological packing embedding anaerobic ammonia oxidation bacteria) embedding anaerobic ammonia oxidation bacteria and activated sludge containing ammonia oxidation bacteria. By using the biofilm reactor, the environmental conditions for nitrification reaction and anaerobic ammonia oxidation denitrification reaction can be simultaneously met, the synergistic effect of the two is enhanced, and the denitrification effect of the CANON process is improved.

[0033] In order to improve the denitrification effect of the CANON process, preferably in the step S31, the dissolved oxygen is controlled to be between 0.2 and 0.8 mg / L, the pH is controlled to be between 7.8 and 8.5, the mixed liquor suspended solids concentration is controlled to be between 2000 and 4000 mg / L, and the hydraulic retention time is controlled to be between 4 and 6 h.

[0034] In the initial pretreatment stage of the denitrification process, the pH value and turbidity of the rare earth tail water are adjusted to obtain a suitable physicochemical environment for subsequent treatment. Preferably, the step S1 comprises: adjusting the pH of the rare earth tail water to 8.0-10, then performing flocculation, and obtaining pretreated tail water after separating the flocculants, preferably controlling the turbidity of the effluent of the step S1 to be ≤5 NTU. For reference Figure 1 The above-mentioned pH adjustment can use sodium carbonate, sodium hydroxide, hydrochloric acid and the like commonly used in the art, and the above-mentioned flocculation treatment can also use inorganic flocculants and organic flocculants commonly used in the art, and specific substances will not be described one by one here.

[0035] In another typical embodiment of the present application, a denitrification system for rare earth tail water is provided, as shown in Figure 2As shown, the denitrification system comprises a pretreatment unit 10, a partial nitrification-anammox denitrification unit 20, and a CANON denitrification unit 30. The pretreatment unit 10 is used for pretreating the rare earth tail water to obtain pretreated tail water. The partial nitrification-anammox denitrification unit 20 is connected to the pretreatment unit 10 and is used for performing partial nitrification-anammox denitrification treatment on the pretreated tail water to obtain primary denitrification wastewater. The CANON denitrification unit 30 is connected to the partial nitrification-anammox denitrification unit 20 and is used for performing CANON process denitrification on the primary denitrification wastewater to obtain denitrified water and sludge. The partial nitrification-anammox denitrification unit 20 comprises a partial nitrification treatment device 21, a first sedimentation tank 22, and an anammox denitrification treatment device 23. The partial nitrification treatment device 21 is connected to the pretreatment unit 10 and has a first mixed liquor outlet and a second mixed liquor reflux inlet. The first sedimentation tank 22 has a first mixed liquor inlet, a concentrated sludge outlet, and a supernatant outlet. The first mixed liquor inlet is connected to the first mixed liquor outlet, and the concentrated sludge outlet is preferably connected to the concentrated sludge reflux inlet. The anammox denitrification treatment device 23 has a supernatant inlet, a second mixed solution outlet, and a primary denitrification wastewater outlet. The supernatant inlet is connected to the supernatant outlet, the second mixed solution outlet is connected to the second mixed liquor reflux inlet, and the primary denitrification wastewater outlet is connected to the CANON denitrification unit 30.

[0036] The denitrification system of the present application uses a multi-step method to denitrify rare earth tail water. First, the rare earth tail water is pretreated to provide suitable water quality conditions for subsequent processing steps. Second, the pretreated tail water is subjected to partial nitrification-anammox denitrification treatment, which is divided into three steps: (1) the rare earth tail water is subjected to partial nitrification treatment to obtain a first mixed liquor containing both ammonia nitrogen and nitrite nitrogen. This step does not require strict control of the ratio of ammonia nitrogen and nitrite nitrogen in the first mixed liquor. (2) Subsequently, anammox denitrification treatment is performed, during which most of the nitrite nitrogen and part of the ammonia nitrogen are removed to obtain a second mixed liquor containing ammonia nitrogen. (3) The second mixed liquor is refluxed to the front-end partial nitrification reaction unit for further nitrification reaction, and this cycle is repeated multiple times to obtain a cycle treatment mixed liquor. Finally, the cycle treatment mixed liquor is subjected to CANON process denitrification treatment to obtain wastewater with ammonia nitrogen and total nitrogen meeting the standards. In the anammox denitrification treatment, most of the unreacted ammonia nitrogen is converted to N2 and removed in the subsequent CANON process, achieving the purpose of wastewater denitrification. Moreover, the above process fully retains the advantages of partial nitrification-anammox, and no organic carbon source needs to be added in this step.

[0037] In the partial nitrification treatment device 21, the ammonia oxidation is controlled in the nitrosation stage to perform the partial nitrification, without the need to strictly control the ammonia nitrogen and nitrite ratio. Moreover, after the partial nitrification treatment device 21, the first mixed liquid obtained is subjected to sludge-water separation A in the first sludge sedimentation tank 22 to obtain concentrated sludge and supernatant, and the sludge is preferably returned to the partial nitrification treatment device 21 to maintain the suspended solid concentration level thereof. After the second mixed liquid is returned to the partial nitrification treatment device 21 for multiple times, the ammonia nitrogen concentration in the wastewater is further reduced to 30 mg / L or less, to form a circulating treatment mixed liquid, so as to enter the CANON denitrification unit 30 for continuous treatment. The embodiment reduces the control difficulty of the partial nitrosation reaction process, and has the advantages of high efficiency, energy saving and flexible regulation.

[0038] Preferably, the CANON denitrification unit 30 comprises a CANON biofilm reactor 31 and a second sludge sedimentation tank 32. The CANON biofilm reactor 31 has a first denitrified wastewater inlet, a third mixed liquid outlet and a sludge return inlet, and the first denitrified wastewater is connected to the partial nitrification-anaerobic ammonia oxidation denitrification unit 20. Preferably, the CANON biofilm reactor 31 is filled with suspended fillers and activated sludge containing ammonia oxidation bacteria, and the suspended fillers embed anaerobic ammonia oxidation bacteria. The second sludge sedimentation tank 32 has a third mixed liquid inlet, a sludge outlet and a denitrified water outlet, and the third mixed liquid inlet is connected to the third mixed liquid outlet, and the sludge outlet is connected to the sludge return inlet.

[0039] In the initial pretreatment stage of the denitrification process, the pH value and turbidity of the rare earth tail water are adjusted to obtain a suitable physicochemical environment for subsequent treatment, as shown in the following formula: Figure 2 As shown, the pretreatment unit preferably comprises an adjusting tank 11 and a coagulation tank 12. The adjusting tank 11 is provided with a pH value adjusting agent feeding device and has an adjusting water outlet. The coagulation tank 12 is provided with a coagulant feeding device and a flocculant feeding device, and has an adjusting water inlet and a pretreated water outlet. The adjusting water inlet is connected to the adjusting water outlet, and the pretreated water outlet is connected to the partial nitrification-anaerobic ammonia oxidation denitrification unit 20.

[0040] The beneficial effects of the present application will be further illustrated in the following examples and comparative examples.

[0041] Example 1

[0042] The implementation process of this embodiment can refer to Figure 1 and Figure 2 .

[0043] 1) The rare earth tail water (ammonia nitrogen concentration = 120 mg / L, pH = 3.2-6.5, COD = 30 mg / L) is used as raw water. The tail water is pretreated in the pretreatment unit 10, and the pretreatment device includes the adjusting tank 11 and the coagulation tank 12. The pH of the tail water is adjusted to 7.5-8.5, and the turbidity is ≤5 NTU, to obtain the pretreated tail water.

[0044] 2) The pretreated tail water enters the partial nitrification-anammox denitrification unit 20 for treatment. The partial nitrification-anammox denitrification unit 20 is a circulating treatment unit including the partial nitrification treatment device 21, the first sludge settling tank 22, and the anammox denitrification treatment device 23. The pretreated rare earth tail water is first subjected to the partial nitrification reaction in the partial nitrification treatment device 21 to obtain the first mixed liquor, and the reaction conditions are DO = 2.0 mg / L (adjusted by aeration), mixed liquor suspended solids concentration MLSS = 3200 mg / L, and hydraulic retention time HRT = 4 h. The obtained first mixed liquor is subjected to the sludge-water separation A in the first sludge settling tank 22 to obtain the supernatant (SS ≤ 20 mg / L) and the concentrated sludge. The concentrated sludge is returned to the nitrification treatment device 21. The supernatant enters the anammox denitrification treatment device 23 for anammox denitrification reaction to obtain the second mixed liquor, and the reaction conditions are DO < 0.5 mg / L (adjusted by aeration), temperature T = 25-28 ℃, mixed liquor suspended solids concentration MLSS = 3800 mg / L, and hydraulic retention time HRT = 2.5 h. When the ammonia nitrogen concentration of the second mixed liquor is > 30 mg / L, part of the second mixed liquor is returned to the front-end nitrification treatment device 21 for circulation treatment, and the circulation ratio of the second mixed liquor is 120%, until the ammonia nitrogen concentration is reduced to ≤ 30 mg / L to obtain the primary denitrification wastewater.

[0045] 3) The primary denitrification wastewater enters the CANON denitrification unit 30 for treatment. The CANON denitrification unit 30 includes the CANON biofilm reactor 31 and the second sludge settling tank 32, wherein the CANON biofilm reactor 31 is filled with the suspended filler and the activated sludge containing anammox bacteria, and the suspended filler embeds the anammox bacteria. The primary denitrification wastewater is subjected to the CANON treatment in the CANON biofilm reactor 31 to obtain the third mixed liquor, and the reaction conditions are DO = 0.8 mg / L, pH = 7.8-8.5, temperature T = 25-28 ℃, mixed liquor suspended solids concentration MLSS = 3600 mg / L, and HRT = 5 h. The third mixed liquor is subjected to the sludge-water separation B in the second sludge settling tank 32 to obtain the sludge and the denitrification water. The sludge is returned to the CANON biofilm reactor 31. The denitrification water has the suspended turbidity SS ≤ 20 mg / L, ammonia nitrogen ≤ 12 mg / L, and total nitrogen ≤ 30 mg / L, which meets the requirements of the Rare Earth Industry Pollutant Discharge Standard (GB 26451-2011).

[0046] Example 2

[0047] The implementation process of this embodiment can refer to Figure 1 .

[0048] 1) This embodiment uses simulated rare earth tail water (ammonia nitrogen concentration = 300 mg / L, pH = 8.5, COD = 30 mg / L) as raw water, without pretreatment.

[0049] 2) The simulated rare earth tail water enters the partial nitrification-anaerobic ammonia oxidation denitrification unit 20 for treatment. The partial nitrification-anaerobic ammonia oxidation denitrification unit 20 is a circulating treatment unit including a partial nitrification treatment device 21, a first sludge settling tank 22 and an anaerobic ammonia oxidation denitrification treatment device 23. The pretreated rare earth tail water is first subjected to a partial nitrification reaction in the partial nitrification treatment device 21 to obtain a first mixed liquor, and the reaction conditions are DO = 2.0 mg / L (adjusted by aeration), mixed liquor suspended solids concentration MLSS = 3800 mg / L, and hydraulic retention time HRT = 1.5 h. The obtained first mixed liquor is subjected to sludge-water separation A in the first sludge settling tank 22 to obtain a supernatant (SS≤20 mg / L) and concentrated sludge. The concentrated sludge is returned to the nitrification treatment device 21. The supernatant enters the anaerobic ammonia oxidation denitrification treatment device 23 for anaerobic ammonia oxidation denitrification reaction to obtain a second mixed liquor, and the reaction conditions are DO < 0.5 mg / L (adjusted by aeration), temperature T = 38-40℃, mixed liquor suspended solids concentration MLSS = 3800 mg / L, and hydraulic retention time HRT = 2.0 h. When the ammonia nitrogen concentration of the second mixed liquor is > 30 mg / L, part of the second mixed liquor is returned to the front-end nitrification treatment device 21 for circulation treatment, and the circulation ratio of the second mixed liquor is 200%, until the ammonia nitrogen concentration is reduced to below 30 mg / L to obtain primary denitrification wastewater.

[0050] 3) The primary denitrification wastewater enters the CANON denitrification unit 30 for treatment. The CANON denitrification unit 30 includes a CANON biofilm reactor 31 and a second sludge settling tank 32, wherein the CANON biofilm reactor 31 is filled with suspended fillers and activated sludge containing ammonia oxidation bacteria, and the suspended fillers embed anaerobic ammonia oxidation bacteria. The primary denitrification wastewater is first subjected to CANON treatment in the CANON biofilm reactor 31 to obtain a third mixed liquor, and the reaction conditions are DO = 0.3 mg / L, pH = 7.8-8.5, temperature T = 25-28℃, mixed liquor suspended solids concentration MLSS = 2600 mg / L, and hydraulic retention time is 10 h. The third mixed liquor is subjected to sludge-water separation B in the second sludge settling tank 32 to obtain sludge and denitrification water. Among them, the sludge is returned to the CANON biofilm reactor 31. The denitrification water has a suspended solids turbidity SS≤20 mg / L, ammonia nitrogen ≤12 mg / L, and total nitrogen ≤30 mg / L, meeting the requirements of the “Rare Earth Industry Pollutant Discharge Standard” (GB26451-2011).

[0051] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0052] The present application adopts a three-step method for denitrification of rare earth tail water. First, a pretreatment unit is used to pretreat the rare earth tail water to provide a suitable reaction environment for the subsequent treatment steps. Second, a partial nitrification-anaerobic ammonia oxidation denitrification unit 20 is used to treat the pretreated tail water by partial nitrification-anaerobic ammonia oxidation denitrification. This treatment is divided into two steps. First, the rare earth tail water is subjected to partial nitrification treatment, and under the action of ammonia-oxidizing bacteria in the form of sludge, O2 is used as an electron acceptor to oxidize part of the ammonia nitrogen in the tail water to generate nitrite nitrogen. Subsequently, anaerobic ammonia oxidation denitrification treatment is carried out, and the anaerobic ammonia oxidation bacteria oxidize ammonia nitrogen using nitrite nitrogen as an electron acceptor, so that nitrite nitrogen and ammonia nitrogen react to form harmless N2 and a small amount of nitrate. This step allows most of the nitrite nitrogen and part of the ammonia nitrogen to be removed, and first denitrification wastewater is obtained. Finally, the first denitrification wastewater is subjected to CANON denitrification in a CANON denitrification unit 30. The CANON denitrification unit 30 converts ammonia nitrogen into nitrogen gas and a small amount of nitrate through the synergistic action of ammonia-oxidizing bacteria and anaerobic ammonia-oxidizing bacteria, forming denitrification water. Most of the unreacted ammonia nitrogen in the anaerobic ammonia oxidation denitrification treatment in the above system will be converted to N2 and removed in the subsequent CANON process, achieving the purpose of wastewater denitrification. Moreover, the above system fully retains the advantages of partial nitrification-anaerobic ammonia oxidation. This equipment does not require the use of a large amount of organic carbon source. In the CANON denitrification unit, the ammonia nitrogen content in the first denitrification wastewater is low, so there is no need for an organic carbon source, thereby reducing energy consumption and operating costs, reducing sludge output, and allowing the denitrification water to be directly discharged as effluent.

[0053] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A denitrification process for rare earth tailwater, characterized in that, The denitrification process includes: Step S1: Pre-treat the rare earth tailwater to obtain pre-treated tailwater; Step S2 involves subjecting the pretreated effluent to partial nitrification-anaerobic ammonia oxidation denitrification treatment to obtain primary denitrified wastewater; and Step S3: The primary denitrification wastewater is subjected to CANON process denitrification to obtain denitrified water and sludge. Step S2 includes: Step S21: Partial nitrification reaction is carried out on the pretreated effluent to convert part of the ammonia nitrogen in the pretreated effluent into nitrite nitrogen, to obtain a first mixed liquid, wherein the dissolved oxygen is controlled between 0.5 and 2.0 mg / L. Step S22: Perform mud-water separation A on the first mixture to obtain concentrated sludge and supernatant; Step S23: The supernatant is subjected to an anaerobic ammonia oxidation denitrification reaction to obtain a second mixture; In step S24, at least a portion of the second mixture is returned to step S21 to continue partial nitrification until step S23, at which point the primary denitrification wastewater is obtained, wherein the ammonia nitrogen concentration of the primary denitrification wastewater is below 30 mg / L. Step S3 includes: Step S31: The primary denitrification wastewater is subjected to CANON denitrification treatment to obtain a third mixed liquid; Step S32: Perform mud-water separation B on the third mixture to obtain sludge and denitrified water, and return the sludge to step S31.

2. The denitrification process according to claim 1, characterized in that, The concentrated sludge is returned to step S21.

3. The denitrification process according to claim 2, characterized in that, In step S21, the pH is between 8.0 and 8.5, the concentration of suspended solids in the mixed solution is between 2000 and 4000 mg / L, and the hydraulic retention time is between 3 and 6 hours.

4. The denitrification process according to claim 2, characterized in that, In step S23, the dissolved oxygen is controlled to be ≤0.5mg / L, the concentration of suspended solids in the mixed solution is between 2000 and 4000mg / L, the hydraulic retention time is between 2 and 4 hours, and the temperature is between 25 and 40℃.

5. The denitrification process according to claim 2, characterized in that, In step S24, the circulation ratio of the second mixture is 50-300%.

6. The denitrification process according to claim 1, characterized in that, Step S31 is carried out in a CANON biofilm reactor (31), which is filled with suspended packing material and activated sludge containing ammonia-oxidizing bacteria, wherein the suspended packing material encapsulates anaerobic ammonia-oxidizing bacteria.

7. The denitrification process according to claim 1, characterized in that, In step S31, the dissolved oxygen is controlled between 0.2 and 0.8 mg / L, the pH is controlled between 7.8 and 8.5, the concentration of suspended solids in the mixed solution is controlled between 2000 and 4000 mg / L, and the hydraulic retention time is controlled between 4 and 6 hours.

8. The denitrification process according to claim 1, characterized in that, Step S1 includes: S11, reduces the turbidity of the effluent through coagulation and sedimentation; S12, adjust the pH of the rare earth tailwater to 8.0~10 to obtain the pretreated tailwater, and control the turbidity of the effluent from step S1 to ≤5 NTU.

9. A denitrification system for rare earth tailwater, characterized in that, The denitrification system is used in the denitrification process of rare earth tailwater according to any one of claims 1 to 8, and the denitrification system comprises: Pretreatment unit (10) is used to pretreat rare earth tailwater to obtain pretreated tailwater; A partial nitrification-anaerobic ammonium oxidation denitrification unit (20) is connected to the pretreatment unit (10) and is used to perform partial nitrification-anaerobic ammonium oxidation denitrification treatment on the pretreatment effluent to obtain primary denitrified wastewater; The CANON denitrification unit (30) is connected to the partial nitrification-anaerobic ammonia oxidation denitrification unit (20) and is used to denitrify the primary denitrification wastewater using the CANON process to obtain denitrified water and sludge. The partial nitrification-anaerobic ammonia oxidation denitrification unit (20) includes: A partial nitrification treatment device (21) is connected to the pretreatment unit (10). The partial nitrification treatment device (21) has a first mixed liquor outlet and a second mixed liquor return inlet. The partial nitrification treatment device (21) also has a concentrated sludge return inlet. The first sedimentation tank (22) has a first mixed liquor inlet, a concentrated sludge outlet and a supernatant outlet. The first mixed liquor inlet is connected to the first mixed liquor outlet, and the concentrated sludge outlet is connected to the concentrated sludge return inlet. The anaerobic ammonia oxidation denitrification treatment device (23) has a supernatant inlet, a second mixed solution outlet and a primary denitrification wastewater outlet. The supernatant inlet is connected to the supernatant outlet, the second mixed solution outlet is connected to the second mixed solution reflux inlet, and the primary denitrification wastewater outlet is connected to the CANON denitrification unit (30).

10. The denitrification system according to claim 9, characterized in that, The CANON denitrification unit (30) includes: The CANON biofilm reactor (31) has a primary denitrification wastewater inlet, a third mixed liquor outlet and a sludge return inlet. The primary denitrification wastewater inlet is connected to the partial nitrification-anaerobic ammonia oxidation denitrification unit (20). The CANON biofilm reactor (31) is filled with suspended packing material and activated sludge containing ammonia oxidizing bacteria. The suspended packing material encapsulates anaerobic ammonia oxidizing bacteria. The second sludge sedimentation tank (32) has a third mixed liquor inlet, a sludge outlet and a denitrified water outlet. The third mixed liquor inlet is connected to the third mixed liquor outlet, and the sludge outlet is connected to the sludge return inlet.

11. The denitrification system according to claim 9, characterized in that, The preprocessing unit includes: The equalization tank (11) is equipped with a pH value adjustment and dosing device and has an equalization water outlet; The coagulation tank (12) is equipped with a coagulant dosing device and a flocculant dosing device, and has a regulating water inlet and a pretreated water outlet. The regulating water inlet is connected to the regulating water outlet, and the pretreated water outlet is connected to the partial nitrification-anaerobic ammonia oxidation denitrification unit (20).

Images